• Srikar Dronamraju's avatar
    uprobes/core: Handle breakpoint and singlestep exceptions · 0326f5a9
    Srikar Dronamraju authored
    Uprobes uses exception notifiers to get to know if a thread hit
    a breakpoint or a singlestep exception.
    
    When a thread hits a uprobe or is singlestepping post a uprobe
    hit, the uprobe exception notifier sets its TIF_UPROBE bit,
    which will then be checked on its return to userspace path
    (do_notify_resume() ->uprobe_notify_resume()), where the
    consumers handlers are run (in task context) based on the
    defined filters.
    
    Uprobe hits are thread specific and hence we need to maintain
    information about if a task hit a uprobe, what uprobe was hit,
    the slot where the original instruction was copied for xol so
    that it can be singlestepped with appropriate fixups.
    
    In some cases, special care is needed for instructions that are
    executed out of line (xol). These are architecture specific
    artefacts, such as handling RIP relative instructions on x86_64.
    
    Since the instruction at which the uprobe was inserted is
    executed out of line, architecture specific fixups are added so
    that the thread continues normal execution in the presence of a
    uprobe.
    
    Postpone the signals until we execute the probed insn.
    post_xol() path does a recalc_sigpending() before return to
    user-mode, this ensures the signal can't be lost.
    
    Uprobes relies on DIE_DEBUG notification to notify if a
    singlestep is complete.
    
    Adds x86 specific uprobe exception notifiers and appropriate
    hooks needed to determine a uprobe hit and subsequent post
    processing.
    
    Add requisite x86 fixups for xol for uprobes. Specific cases
    needing fixups include relative jumps (x86_64), calls, etc.
    
    Where possible, we check and skip singlestepping the
    breakpointed instructions. For now we skip single byte as well
    as few multibyte nop instructions. However this can be extended
    to other instructions too.
    
    Credits to Oleg Nesterov for suggestions/patches related to
    signal, breakpoint, singlestep handling code.
    Signed-off-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
    Cc: Linux-mm <linux-mm@kvack.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/20120313180011.29771.89027.sendpatchset@srdronam.in.ibm.com
    [ Performed various cleanliness edits ]
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    0326f5a9
thread_info.h 8.91 KB